Metallothionein (MT) is a low molecular weight cysteine rich intracellular protein which binds with divalent metals. High concentrations of zinc (Zn) bound to MT have been isolated from livers of fetal and newborn mammals. However, MT is rapidly degraded during postnatal development and only trace amounts are detected in adult liver. Recently our preliminary studies on immunohistochemical localization of MT by peroxidase-antiperoxidase method using a specific antibody to MT have revealed that there are differences in its disposition in hepatocytes of newborn and adult rats. In newborn rats, MT is mainly localized in the nucleus of hepatocytes while adult rat hepatocytes contained trace amounts of MT exclusively in the cytoplasm. The specific aims of the proposal are to extend these studies to define various factors which may influence these nuclear-cytoplasmic translocations of Zn and MT and also its effects on the cellular functions. We will study specifically the changes in MT (both content and localization), DNA dependent RNA polymerase (nuclear effect) and protein biosynthesis (cytoplasmic effect) during postnatal developement and Zn deficiency (adult and newborn). We will also develop techniques to localize MT in tissues at the subcellular level by electron microscopy using a protein A-gold procedure. Since rat liver contains three types of DNA dependent RNA polymerase, it will be interesting to study the effect of Zn deficiency and presence of high concentration of ZnMT in the nucleus on these individual RNA polymerases and their subsequent effect on gene expression. Studies will also be undertaken in isolated systems such as primary cell cultures (rat liver and kidney) and cell free systems to accomplish some of these objectives. These studies will provide valuable insights into the physiological function of MT in Zn metabolism and the probable role for this protein in cellular growth during postnatal development and in Zn deficiency in mammals.